Several attempts have been made to design a spinal prosthesis for replacement of missing or excised disk material that replicates the functions of the missing tissue. U.S. Pat. No. 4,759,769 to Hedman et al discloses a two piece artificial disk device in which two plates are attached to the adjacent vertebrae by bone screws inserted through flanges on the plates. A spring biasing mechanism is captured between the plates to simulate the actions of the natural disk material. U.S. Pat. No. 5,246,458 to Graham and U.S. Pat. No. 6,228,118 to Gordon disclose other intervertebral implants with arcuate flanges used to connect the device to adjacent vertebra.
The patents to Marnay, U.S. Pat. No. 5,314,477, Buttner-Janz et al, U.S. Pat. No. 5,401,269, Yuan et al, U.S. Pat. No. 5,676,701, and Shelokov, U.S. Pat. No. 6,039,763, all are directed to the design of the opposing faces of the adjacent plates of an implant to provide a limited universal joint to simulate the natural movement of the spine.
U.S. Pat. No. 5,683,465 to Shinn et al teaches two plates with bow shaped skirts which are interlocked.
What is needed in the art is a disk prosthesis that has limited universal motion yet is securely interlocked to prevent dislocation or separation.